Policy management in an IP network is an important function as the policies indicate essential conditions for the users in the network.
An example of an IP network is IP Multimedia Subsystem (IMS). IMS has been developed by the 3rd Generation Partnership Project (3GPP) as an open standard, to give operators of access networks the ability to offer multimedia services in the packet domain. An IMS network can be built above any type of access network and is more or less independent of the access technology used. By using IMS, telecommunications operators can provide services to users irrespective of their location, access technology, and terminal. It also includes a handover of calls between fixed-line and mobile networks.
An important function of IP networks is the enforcement of different policies. These policies dictate e.g. what particular users may and may not do, what they will be charged or what Quality of Service (QoS) a particular user will receive for a specific service. Policies are enforced using policy “rules”. A single policy may require a set of policy rules. Policy rules are installed into a node through which all traffic of the users pass or into multiple nodes, which collectively handle all traffic of the user. Common functions in a policy management system are a Policy Enforcement Point (PEP), a Policy Decision Point (PDP) and a subscriber database comprising subscriber/subscription related information.
In 3GPP the PDP functions are handled by the Policy and charging Rules Function (PCRF), the PEP functions are handled by the PCEF located in the GGSN and the subscriber database functions are handled by the Subscription Profile Repository (SPR).
For large IP networks it is common to have several PEPs and several PDPs. Each operator has normally at least one subscriber database for their users. An important function in a case of an IP network is the possibility of roaming and handover between different access points and access networks. Roaming occurs when a user of one service provider or operator uses the facilities of another service provider or operator. Handover normally means the transfer of an ongoing call or data session from one channel connected to the network to another.
From a policy management point of view a Mobile Terminal access the IP network via a PEP which is associated to a specific PDP, which controls the PEP.
For e.g. reasons of scalability, each operator could have several PDP in his network. It is also possible that an operator has a specific PDP for a certain access, e.g. one PDP for 3GPP access and another one for WiMAx access. If a visited network or a home network comprises several PDPs there is no solution today that can handle the policy management in roaming and handover between different PEPs.
In 3GPP R7 a mobile terminal accesses the IP network via a PCEF, a PEP, and the IP address of the subscriber will be associated to a PCRF, a PDP, which controls to the PCEF. If the IP Connectivity Access Network (IP-CAN) is GPRS the appropriate PCRF could be contacted based on which Access Point Name (APN) the mobile terminal is connected to. It is also possible to use the IP address to choose the appropriate PCRF.
For other IP-CANs the Gateway shall contact the appropriate PCRF based on the access point the mobile terminal is connected to and, optionally, a mobile terminal identity information that is applicable for that IP-CAN. In the case of GPRS the mapping from a certain user equipment identity and/or access point name to the PCRF is typically stored in pre-configured tables in the GGSN, the PCEF and the AF.
If there is a plurality of PCRFs in a network the policy management will not work properly. If the mobile terminal has the possibility to access the network via different access points and access networks controlled by different PDPs, different nodes associated to the mobile terminal does not know which PDP that controls the policy management of a mobile terminal.
Other architectures have similar functions as the PCRF, e.g. TISPAN, WiMax Forum, DSL Forum and PacketCable. They also have similar solutions to associate an end-user to a specific PDP.